1. Field of the Invention
The present invention relates to a material essentially comprising a spin transition compound, to processes for the preparation of said material and to various applications of the material.
2. Description of Related Art
It is known to use compounds which exhibit a spin, transition for various applications, in particular for information storage. Such compounds can in particular be coordination complexes comprising one or more metal centers having a 3d4, 3d6 or 3d7 configuration, one or more nitrogenous ligands and one or more anions, such as described, for example, in EP-0 543465, EP-0 666 561, EP-0 745 986 and EP-0 842 988.
EP-0 543 465 describes a process for the preparation of spin transition compounds and the use for information storage. The process consists in bringing together, on the one hand, the ligand and, on the other hand, an iron salt in an acid solution, in allowing to react, in order to obtain a precipitate, and in recovering the precipitate in the powder form. For the use for data storage, the complex obtained is reduced beforehand to a powder in order to be deposited on a support by various methods. The compounds mentioned correspond to one of the following formulae: FeL3(NO3)2 in which L is a ligand of the 1,2,4-triazole or 4-amino-1,2,4-triazole type, in combination with the NO3− anion; Fe(ATP)2.5Cl2, in which the ATP ligand is 4-amino-1,2,4-triazole in combination with Fe(II) and with Cl−; Fe(TP)2Cl2 in which the TP ligand is 1,2,4-triazole, in combination with Cl−; [Fe(2-aminomethylpyridine)3]Cl2EtOH, EtOH being ethanol; [Fe(1,10-phenanthroline)2](NCS)2; [Fe(1-propyltetrazole)6](BF4)2; complexes of a metal M in combination with a mixture of several ligands (chosen from R-Trz, amines NL2 and triazolates Trz-, M being Fe(II), Fe(III) or Co(II), R-Trz being a triazole carrying an R substituent, R and L being an alkyl or H) and with an anion chosen from BF4−, ClO4−, CO32, Br− and Cl−, the complex additionally comprising a defined amount of water.
With the exception of [Fe(1,10-phenanthroline)2(NCS)2], all these complexes are pink in color in the low spin (LS) state and white in the high spin (HS) state. The transition is brought about by heating or cooling and takes place between −20° C. and 100° C. These compounds exhibit a phenomenon of hysteresis which can range from a few degrees to a few tens of degrees.
EP-0 666 561 describes spin transition compounds which correspond to the formula Fe(II)(H-Trz)3(X)2 in which Trz is 1,2,4-triazole and (X)2 represents the anion (BF4−)2, (ClO4−)2, (Br−)2, (Cl−)2 or (CO32−). These compounds exhibit two crystalline phases, each having spin transitions associated with a change in color (white/pink) and for which the temperatures T1/2↓ and T1/2↑ are respectively less than and greater than ambient temperature. The preparation process is analogous to that described in EP-0 543 465 above.
EP-0 745 986 describes compounds corresponding to a formula analogous to that of the compounds of the “complex of a metal M in combination with a mixture of several ligands” type described in EP-0 543 465, M being here a metal ion of d5, d6 or d7 configuration, the ligand being a dialkylaminotriazole and the anion comprising a sulfitoaryl, sulfitoalkyl, sulfitoaryl halide or sulfitoalkyl halide group. These specific compounds here a hysteresis amplitude of greater than 70° C. and a region of bistability centered exactly around ambient temperature. Said compounds are pink in the LS state and white in the HS state. The process for the preparation of the compounds, described very briefly, is analogous to that described in EP-0 543 465 above.
EP-0 842 988 describes spin transition chemical compounds and their use in display devices where a temperature threshold is exceeded. The compounds are formed by a network composed of molecules each formed by a metal-ligand complex and by an anion, and they comprise at least one water molecule bonded to the ligand via a hydrogen bond. The metal is chosen from those which have a d4, d5, d6 or d7 configuration. The ligand is 1,2,4-triazole carrying an R substituent comprising an OH group. The anions are nitrate and tosylate derivatives. The compounds corresponding to this definition have a temperature T1/2↑ of between 80 and 95° C. and a T1/2↓ of −170° C. They can be used in particular in devices intended to detect an accidentally high (of the order of 80° C.) storage temperature in storage buildings or transportation vehicles. The compounds are prepared by mixing a precursor of the metal center and a precursor of the ligand, at ambient temperature, and by removing the solvent by filtration after a precipitate has been obtained. The compound is obtained in the pulverulent form.
WO-06/002651 describes a material composed of nano-particles of complexes of iron, of a triazole ligand and of at least one anion. This material, as a result of its nanometric nature, is of particular use especially as thermochromic pigment or for data storage.
Koningsbruggen Van P. et al. [Journal of Material Chemistry, The Royal Society of Chemistry, Cambridge, GB, vol. 7, No. 10, 2069-2075] describe compounds which correspond to the formula [Fe(NH2trz)3]X2.xH2 in which either the two X groups are noncoloring anions, such as NO3−, ClO4−, Br− and others, or the two X groups are anions which have coloring properties, in particular naphthalene anions carrying an SO3− group. The color of these compounds changes from crimson-pink to white during heating to approximately 370K.
However, all these materials of the prior art specified have a very limited range of color variations since, depending on their spin state, they are either pink or crimson, on the one hand, or white, on the other hand.
A few compounds are known for which a rise in temperature brings about a change in color other than “pink-white”. For example, Arslan et al. [Dyes and Pigments, Elsevier Applied Science Publishers, Barking, GB, vol. 75, No. 3, 521-525] describe a complex [Zn(Hsal)2(H2O)(abpy)].H2O which changes from brown to crimson during heating. “abpy” represents azobis-pyridine. In these compounds, the change in color is not due to a spin transition but to a phase transition, which is a relatively slow phenomenon, whereas spin transition is a rapid and virtually inexhaustible phenomenon in the solid phase.
Kume Shoko et al. [Chemical Communications, No. 23, 2006, 2442-2444] describe an FeII triazole complex [Fe(1)3(BF4)2] corresponding to the formula
which changes from yellow to orange. This compound certainly makes possible a change in color other than “pink-white”. However, the change in color originates not from a spin transition but from a photo-isomerization of the ligand at a given temperature which modifies the absorption of the compound. The change in color occurs without hysteresis and cannot be adjusted.